1. Field of the Invention
The present invention relates to a press-fit sealed electronic component and a method for producing the same.
2. Description of the Related Art
Electronic components such as a quartz oscillator are hermetically sealed in a predetermined package so that the operating environment is stably kept clean. According to Japanese Unexamined Patent Application Publication No. 09-260990 (pp. 2-3, FIG. 1), the surface of a sealing tube formed by press working is planarized by a chemical treatment. This technology does not require a step of plating, and in addition, prevents the leakage caused by press-fitting a plug. Japanese Patent No. 2,586,981 (p. 2, FIG. 1) discloses a technology for producing a pressed component composed of nickel silver having excellent luster and good quality at a relatively low cost. In this technology, a metal cover of, for example, a quartz oscillator, the cover composed of nickel silver formed by press working, is annealed in a controlled atmosphere so that zinc (Zn) is thickened at the surface. Furthermore, according to a technology disclosed in Japanese Unexamined Patent Application Publication No. 10-150115 (pp. 2-3, FIG. 1), a nickel (Ni) layer formed by plating on the surface of a nickel silver sheet is recrystallized by heat treatment in order to prevent fracture of the nickel plated layer during a subsequent deep drawing process to form a sealing case.
However, in the known art described in Japanese Unexamined Patent Application Publication No. 09-260990, the periphery of the plug, which is to be press-fitted in the sealing tube is plated with copper as an underlayer, and the copper layer is then plated with solder (i.e., tin-lead alloy) in order to improve airtightness by press-fit. Since the plug is press-fitted in the sealing tube while the solder plating layer is scraped, internal stress remains in the scraped plated pieces. Therefore, whiskers (needle-like crystals) generated by the internal stress causes a problem. Even if the internal stress is relieved by annealing, the whiskers are generated due to tin (Sn) in the solder plating layer. Unfortunately, contact between the whiskers and a quartz oscillator deteriorates the characteristics of the quartz oscillator.
In addition, lead (Pb) in the solder plating layer worsens the working environment of the plating. Even when a lead-free alternative material such as an alloy of tin and copper is used for plating, whiskers are generated due to the tin. The use of the alternative material also causes the same problem. Furthermore, the inventions disclosed in Japanese Patent No. 2,586,981 and Japanese Unexamined Patent Application Publication No. 10-150115 do not contribute to the improvement of the air-sealing between the sealing tube and the plug.